1. Field of the Invention
This invention relates to a method for preparing hydrogenated and functionalized polymers and to the hydrogenated products thus obtained. More particularly, this invention relates to a method for preparing hydrogenated polymers which contain acidic functional groups which normally interfere with hydrogenation and to the hydrogenated products containing such functional groups.
2. Prior Art
Polymers containing ethylenic unsaturation and both aromatic and ethylenic unsaturation are, of course, well known in the prior art. Frequently, polymers of this type are prepared by polymerizing one or more polyolefins, particularly diolefins, either alone or in combination with one or more alkenyl aromatic hydrocarbons. Polymers of this type are taught, for example, in U.S. Pat. Nos. 3,135,716; 3,150,209; 3,321,635; 3,265,765; 3,322,856; 3,496,154; 3,498,960; 4,145,298 and 4,328,202. As is well known, copolymers containing both aromatic and ethylenic unsaturation may range from plastic to elastic depending, inter alia, upon the relative amount of polyolefin and alkenyl aromatic hydrocarbon monomer units contained therein.
The use of polymers containing ethylenic unsaturation and both aromatic and ethylenic unsaturation, particularly elastomeric polymers, as a modifier in polymeric compositions containing thermosetting polyesters as well as in polymeric compositions containing various engineering thermoplastics is also well known in the prior art. Compositions of this type containing thermosetting polyesters are taught, for example, in the Background section of U.S. Pat. Nos. 4,329,438. Compositions of this type containing various engineering thermoplastics are taught, for example, in the Background section of U.S. Pat. No. 4,628,072. In general, polymers initially containing ethylenic or ethylenic and aromatic unsaturation may be either a major or minor component in the polymeric composition. As is also well known, however, when the unsaturated polymer is simply admixed with a thermosetting or thermoplastic polymer in a molding composition, destructive phase separation frequently occurs as does rubber bleeding to the surface during curing or setting. Moreover, when the unsaturated polymer is used directly, o neat, shaped products prepared from the compositions generally exhibit poor weatherability and poor thermal stability.
Recently, it has been discovered that destructive phase separation (incompatibility) and the problems associated therewith can be eliminated or at least significantly reduced if the polymer containing ethylenic unsaturation or both aromatic and ethylenic unsaturation is functionalized prior to its incorporation into a composition containing a thermosetting or thermoplastic polymer. Such functionalization is taught, for example, in U.S. Pat. Nos. 4,329,438; 4,578,429 and 4,628,072. In general, functionalization is accomplished by incorporating one or more functional groups, particularly carboxylic acid groups or a derivative thereof into the polymer. In general, functionalization with a carboxylic acid group, particularly a polycarboxylic acid, is considered to be most advantageous.
As is well known, polymers containing ethylenic unsaturation may be functionalized thermally through the so-called ENE reaction wherein an ethylenically unsaturated functionalizing agent, particularly a dicarboxylic acid, is grafted onto the polymer at a carbon atom which is allylic to an ethylenic unsaturation contained therein. Functionalization may also be accomplished via free-radical grafting of an ethylenically unsaturated carboxylic acid onto the polymer, said ethylenically unsaturated functionalizing agent adding across a double bond contained in the polymer. The free-radicals required for such grafting may be imparted either thermally or with a free-radical initiator. Of these methods, incorporation of a functional group via the so-called ENE reaction is frequently preferred since it tends to result in the incorporation of a single functional group at each point of incorporation whereas the methods involving the use of a free-radical tend to incorporate an oligomer of the functional group monomer unit. Moreover, the so-called ENE reaction can be accomplished without any significant coupling while the free-radical methods generally result in significant coupling, particularly when the polymer contains significant amounts of ethylenic unsaturation when the reaction is accomplished. Carboxylation of a polymer containing ethylenic unsaturation or a polymer containing ethylenic unsaturation and aromatic unsaturation may also be accomplished by first metallating the polymer, then reacting the metallated sites with a carboxylating agent such as CO.sub.2. When the metallated polymer contains both ethylenic and aromatic unsaturation, the functionality will, generally, be distributed in a manner proportionate to the relative number of ethylenically unsaturated sites and aromatic rings contained in the polymer. When a polymer is functionalized by metallating followed by reaction with a suitable electrophile, only one functional group can be incorporated at each site of incorporation and coupling generally is not significant. Functionalized polymers containing a significant amount of ethylenic unsaturation still exhibit poor weatherability and poor thermal stability.
It has also recently been discovered that both the weatherability and thermal stability of ethylenically unsaturated polymers can be improved by hydrogenation of at least a portion of the ethylenic unsaturation. Hydrogenation of these type polymers also makes them useful as oil additives, particularly as viscosity improvers. Methods for hydrogenating ethylenically unsaturated polymers are, of course, well known in the prior art. For example, methods for nonselectively hydrogenating polymers containing both ethylenic and aromatic unsaturation are taught in U.S. Pat. Nos. 3,113,986; 3,595,942 and 3,700,633 while processes for selectively hydrogenating ethylenic unsaturation in polymers containing both ethylenic and aromatic unsaturation are taught in U.S. Pat. Nos. 3,634,549; 3,670,054; 3,700,633 and U.S. Pat. No. Re. 27,145. These methods may, of course, be used to hydrogenate polymers containing only ethylenic unsaturation. These processes cannot, however, be used to hydrogenate polymers containing certain acidic functional groups which would interfere with the hydrogenation reaction such as carboxyl groups and the like. The reason or reasons for the inoperability of these several processes with such functionalized polymers is, of course, not well known, but it is believed due to a chemical reaction between the metal or metal compounds contained in or used to prepare the catalyst and the functional groups, which reaction effectively deactivates the catalyst. Also, when the catalyst is prepared with a metal compound containing a cation capable of complexing with the functional group, gelling of the polymer solution is frequently encountered.
Processes for hydrogenating polymers containing ethylenic unsaturation and carboxyl functionality are, of course, also known in the prior art. For example, it is known to use supported and unsupported metals such as palladium as catalysts as taught, for example, in U.S. Pat. Nos. 3,793,274; 4,460,724; 4,129,557; and 4,010,130; and U. K. Patent. No. 1,356,309. It is also known to use catalysts such as thorium complexes as taught, for example, in U.S. Pat. Nos. 4,631,315 and rhodium complexes as taught, for example, in U.S. Pat. Nos. 3,700,637 and 4,647,627 and U. K. Patent No. 1,558,491. These catalysts are not, however, generally, practical for large scale commercial operations where catalyst recovery is inefficient as in polymer hydrogenation processes. In this regard, it should be noted that these precious metals are available in limited supply which makes them very costly when compared to metals commonly used in polymer hydrogenation processes.
Since there are several well known advantages associated with both an acidic functionalized, particularly a carboxylated, and hydrogenated polymer, it has, heretofore, been expedient to first hydrogenate the ethylenically unsaturated polymer and then functionalize the same. Once the ethylenically unsaturated polymer has been hydrogenated, however, the methods which can be used for functionalization are reduced. It will, of course, be appreciated that to the extent that the hydrogenated polymer contains a significant amount of residual ethylenic unsaturation, any of the techniques heretofore noted could be used. If the hydrogenation of the ethylenic unsaturation has, however, been completed or substantially completed, incorporation of functionality via the so-called ENE reaction as well as by free-radical addition of an ethylenically unsaturated functionalizing agent across an ethylenically unsaturated site is no longer possible. Functionalization may, of course, be accomplished in selectively hydrogenated copolymers containing aromatic unsaturation using the method described in U.S. Pat. No. 4,145,298 but metallization of such a polymer followed by reaction with a functionalizing agent will incorporate the functionality exclusively into the aromatic portion of the polymer. This method is, of course, frequently used today and polymeric compositions containing such functionalized polymers do offer several advantages. More recently, however, the desirability of having at least some acidic functionality in the elastic portion of the polymer has been discovered. Functionalization may also be accomplished by the method described in U.S. Pat. No. 4,578,429, a method believed to impart functionality into the elastomeric portion of such hydrogenated polymers by free-radical grafting of an ethylenically unsaturated compound onto the polymer. Such free-radical grafting, however, results in degradation of the polymer. When the polymer is a block copolymer containing, for example, terminal polymeric blocks comprising monoalkenyl aromatic hydrocarbon monomer units and a central polymeric block containing conjugated diolefin monomer units, which block would be elastic, cleavage of the block copolymer within the elastomeric (central) block can destroy or at least reduce the advantages otherwise associated with the use of such a polymer. Also, when the method of U.S. Pat. No. 4,578,429 is used to incorporate the desired functionality, the functionality is believed to be concentrated at a limited number of sites as oligomers of the monomer unit used as a source of the functional group rather than distributed somewhat uniformly along the polymer chain. Moreover, the amount of functionality incorporated into the polymer with this particular method is difficult to control and the length of the oligomer is generally longer than that which would be incorporated into an unsaturated polymer due to the reduced number of sites available for reaction. In light of this, the need for an improved process for preparing hydrogenated polymers containing acidic functional groups that interfere with the more commonly used hydrogenation catalyst, particularly a process wherein at least some such functionality can be incorporated into an elastomeric portion of the polymer without degrading the same, and for the products thereof is believed to be readily apparent.